Semiconductor based light emitting diodes (LEDs) are among the most efficient light sources available today. LEDs provide longer lifetime, higher photon flux efficacy, lower operating voltage, narrow-band light emission, and flexibility in terms of assembly compared to conventional light sources.
Hence, it is often desirable for practical as well as aesthetical reasons to use LEDs in luminaires for general lighting purposes and functional light in public spaces, buildings, offices, homes etc.
The light output of a LED light source is generally not sufficient for most applications, and several LED light sources have to be combined to generate sufficient light levels. Increasing the number of LED light sources in a LED luminaire is, however, not straight forward as LED luminaires are not easily scalable in size or light output. Hence, the design of the LED luminaire has to be changed when more or fewer LEDs are required.
The fact that the LED light source is a small, high brightness light source presents opportunities as well as challenges. On the one hand the small size of the LED light sources allows for LED luminaires having a compact design, but on the other hand it is challenging to obtain an efficient light distribution within the LED luminaire and to avoid high brightness spots appearing in the LED luminaire.
A LED luminaire may further comprise wavelength converting materials in order to produce, for example, white light using LEDs emitting blue or ultra-violet light. The efficiency of such a LED luminaire is often limited by light absorption in the LED light source such that the amount of light received by the wavelength converting material is reduced. This results in reduced efficiencies for the LED luminaires.
JP 2007 173177 A discloses a lighting device comprising an LED emitting light into a light guide wherein a light exit surface of the light guide is provided in a reflector which collimates and directs the light exiting from the light guide.